With a cartridge that houses printing material supplied to a printing device, for example, cartridges for supplying ink as one example of a printing material to an inkjet printer as one example of a printing device are known. With this kind of cartridge, normally, an ink supply port for supplying ink to the outside is provided. As modes of the supply port, various items are known, but as an example of this, items are known for which a porous member is provided by which ink inside a chamber is transferred to the inkjet printer (see U.S. Patent Application Publication No. 2008/204526, for example). As with U.S. Patent Application Publication No. 2008/204526, with a cartridge that leads ink via the porous member, there are cases when the space of the supply port interior is made to communicate with air. By having the space of the supply port interior communicate with air, for example when the supply port is blocked, such as when the cartridge is mounted in the printer, for example, even if the air existing in the space of the supply port interior is expanded by a temperature change or the like, the expanded portion of air is released to the outside, so it is possible to suppress to a low level the pressure fluctuation in the space of the supply port interior. Also, when the supply port is blocked such as when the cartridge is mounted in the printer or the like, even in a case such as when the air existing in the space of the supply port interior is rapidly compressed, the compressed air is released to the outside, so it is possible to suppress to a low level the pressure fluctuation in the space of the supply port interior. In this way, if it is possible to suppress to a low level the pressure fluctuations in the space of the supply port interior, it is possible to prevent the air existing in this space from flowing into the chamber via the porous member, or flowing into the inkjet printer. With the cartridge of U.S. Patent Application Publication No. 2008/204526, an opening is provided on the porous member. This opening is connected to a ventilation path provided on the cartridge interior, and this ventilation path is connected to an air communication port. Specifically, with the cartridge of this publication, the space of the supply port interior is in communication with the air via the opening provided on the porous member, the ventilation path provided on the cartridge interior, and the air communication port.